I think Node-RED dev doc is already very good. I've came from C++ world, in 2-3 days I have integrated a custom system into Node-RED, learning about nodejs, npm, js, and node-red user and dev docs included :). No other IoT system was as friendly as NR, when talking about plugins.
There could be much more info in documentation, I agree with that, but for me (as newbie) I think, the most important things should stay on top, so the docs stays short and easy to read and understand. More advanced information maybe hidden in spoilers or something.
The second, very important thing is that the doc should always stay in sync with the code. Many other systems I have test before NR has very bad doc, caused by differences between current version and documentation. And that simply kills over a half of newbies like me ;).
Good Job so far NR-team ;]